Reverse osmosis membrane treatment system and reverse osmosis membrane treatment method

A reverse osmosis membrane treatment system comprising:

• a first reverse osmosis membrane treatment unit for passing treatment target water through a first reverse osmosis membrane to obtain first permeated water and first concentrated water;
• at least a second reverse osmosis membrane treatment unit for passing the first permeated water through a second reverse osmosis membrane to obtain second permeated water and second concentrated water;
• and
• a pretreatment system configured to pretreat a raw water, the pretreatment system being provided upstream of the first reverse osmosis membrane treatment unit;
• wherein
• a permeation flux per 1 MPa of effective pressure in the second reverse osmosis membrane is in a range of from 15% to 45% of a permeation flux per 1 MPa of effective pressure in the first reverse osmosis membrane, and a permeation flux per 1 MPa of effective pressure in the second reverse osmosis membrane is 0.5 m3/m2/d or less,
• the effective pressure is determined in accordance with JIS K3802:
• 2015 and the permeation flux is obtained by dividing an amount of permeated water by a membrane area,
• the treatment target water contains a substance to be removed selected from at least one of boron, urea, and tetraalkylammonium salts,
• the substance to be removed is removed by the second reverse osmosis membrane,
• the second reverse osmosis membrane is a membrane modified with an oxidant, and
• an oxidant adding pipe is further provided to the pretreatment system and is configured to add the oxidant to at least the pretreatment system and a raw water supply pipe, through which the raw water is supplied to the pretreatment system.